The Savonius vertical axis wind turbine is the definitive drag type vertical axis wind turbine. It uses a plurality of curved vanes which are mounted for rotation about a substantially vertical axis. In most conventional Savonius rotors, only two vanes are provided, and the vanes have generally an S-shape when viewed from above or below. Although invented in the 1920s (see U.S. Pat. Nos. 1,697,574 and 1,766,765, for example), and despite its numerous advantages (including high torque, simplicity of construction, no need for speed limiting, not significantly affected by turbulence, the ability to self-start at very low wind speed, and no need to orient it into the wind—that is it is “omni-directional”), the Savonius wind turbine has never been marketed on a Significant commercial scale. Most are home made (see Making a simple Savonius wind turbine by Lance Turner, at web site ata.org.au: Savonius Rotor Construction: Vertical Axis Wind Machines From Oil Drums by Jozef Kozlowski Vita Publications, 1977; and Savonius Wind Turbine by Denkins, at web site denkins.net/dustin/windturbine.htm) with rigid supports on the top and bottom of each set of vanes. However, there are three common conventional types (as described in the Turner article).
The first common conventional type uses a central shaft to provide the majority of the support for the vanes. This design has the advantage of allowing the rotor to be supported only from the bottom, and can minimize weight. However, it does not have optimum efficiency.
The second and third common conventional types (differing from each other only in the particular curvatures of the vanes) allow spillover of the wind from one vane to another by horizontally spacing the proximate ends of the vanes. However, this conventionally requires utilizing disc shaped solid supports above and below the vanes, and mounting structures both above and below the unit. This increases cost and limits the versatility of the units. Another type of vertical axis wind turbine, which has individual Savonius rotors but mounted so that it has only some features in common with a conventional Savonius, is disclosed in U.S. Pat. No. 4,830,570. This patent shows a rotor having bearings connected to support arms at both the top and bottom of the curved blades (vanes) and a solid exterior single central shaft remote from (not adjacent) the interior blade vertical edges (proximate edges) of both blades. In this construction the central shaft can actually interfere with the spillover of wind from one blade to the other, and likely will unless the blades are horizontally spaced from each other a distance that may not be optimum for efficiency. Also, in this patent the Savonius wind turbine desirable feature of omni-directionality is eliminated by mounting two rotors on horizontally spaced vertical axes with a deflector plate between them, and a partition plate with tail extending perpendicular to the deflector plate to orient the assembly into the wind.
According to the present invention, a full-advantage (including omni-directionality) Savonius vertical axis wind turbine and rotor therefor (that is one having a plurality of curved vanes, typically two or three, with proximate substantially vertical edges horizontally spaced from and overlapping each other) is provided which has the strength, versatility, and simplicity advantages of the first conventional type described above, yet has approximately the efficiency of the second and third conventional types (depending upon vane construction). This is accomplished by providing a substantially vertical central shaft construction positioned adjacent the proximate edges of the vanes and operatively connected to the vanes and mounting the vanes, during use, so that there is spillover of wind from the proximate edge of one vane to the other vane during powered rotation thereof in response to wind. (The term “operatively connected”, and modifications thereof, as used herein means what it normally does any suitable connection that allows the components to function properly.) While any central shaft construction that achieves these results may be provided, two suitable alternatives are a single substantially vertical perforated shaft connected to both vanes (including, perhaps, along the proximate edges thereof), or first and second horizontally spaced substantially vertical shafts one adjacent each of the proximate edges of the vanes. From tests constructed of a model of the Savonius rotor according to the invention—compared to one with a single central shaft and/or heavy upper and lower plate constructions—one can expect both increased torque and increased rpm at both low (e.g. about 7 mph) and moderate (e.g. about 17 mph) wind speeds. In one test the maximum rpm was almost 50% greater, and the maximum torque increased more than 50%.
While typically the vanes of the rotor according to the invention have a simple curvature (that is are curved only about a substantially vertical axis), they may have complex curvatures (that is curved about multiple axes, such as defining a generally helical surface). The vanes may also be tapered vertically, for example having a larger horizontal dimension at the bottom, or alternatively at the top, and may be provided in sets stacked one above the other with the vanes of the stacked sets either aligned, or preferably angularly offset from each other (e.g. about 15-90 degrees, preferably about 30-60 degrees). While the Savonius rotors according to the invention have the advantage of not necessarily requiring a support at the top of the central shaft construction, such a top support may be provided where desired and cost-effective. The rotors can be connected up to almost any type of driven device including (without limitation) a water propeller, a pump movable element, an electrical generator, or a fan blade.
According to one aspect of the present there is provided an omni-directional Savonius vertical axis wind turbine rotor comprising: First and second curved vanes having remote substantially vertical edges widely spaced from each other, and proximate substantially vertical edges more closely horizontally spaced from each other and horizontally overlapping. And, a substantially vertical central shaft construction operatively connected to the vanes and mounting the vanes and adjacent the proximate edges so that, during use, there is spillover of wind from the proximate edge of one vane to another vane during powered rotation of the vanes in response to wind.
In one variant, the shaft construction comprises a single substantially vertical perforated shaft connected to both vanes.
In another variant, the shaft construction comprises first and second (or more) horizontally spaced substantially vertical shafts adjacent the proximate edges of the first and second vanes, respectively. This variant may further comprise vertically spaced first and second substantially horizontally extending connecting elements which connect the first and second (or more) shafts together without significantly interfering with spillover of wind from one vane to the other.
The wind turbine rotors as recited above may be in combination with a mount which mounts the shaft construction and vanes for rotation about a substantially vertical axis, and for operative connection of the shaft construction to a powered element, to provide a wind turbine. In the multiple-shaft embodiment, the mount may comprise a single shaft element adjacent bottom portions of the shafts and operatively attached to the shafts so that the turbine is substantially devoid of a top mount for the rotor; and the single shaft element may be connected to the first and second shafts by attachment to the first connecting element. The turbine may be in combination with a powered element comprising an electrical generator, a water pump movable element, a fan blade, or a water propeller, operatively connected to the mount; and the vanes may have a complex curvature.
In either variant of the Savonius vertical axis wind turbine rotor a third (or more, although more than three is usually less desirable than two or three) vane may be provided. For example, the multi-shaft variant may further comprise a third curved vane having remote and proximate substantially vertical edges, and the shaft construction may comprise a third substantially vertical shaft operatively connected to the third vane so that the proximate ends of the first, second, and third vanes are spaced from each other and, during use, there is spillover of wind from each vane to another during rotation of the shafts.
The Savonius vertical axis wind turbine rotor may further comprise substantially rigid spokes operatively connected to top and/or bottom portions of the vanes and extending substantially radially outwardly from the central shaft construction. Also, the vanes may be made of flexible, collapsible, material, and may include removable battens, and the spokes may move along the shaft construction. Further, there may be provided remote support elements for supporting the remote substantially vertical edges of the vanes, and connected to the spokes. As another alternative, the vanes may be of relatively rigid, substantially non-collapsible, material, with the vanes operatively connected to the central shaft construction adjacent the proximate ends thereof.
The first and second vanes may comprise a first set, and the rotor may further comprise a second set of vanes associated with the central shaft construction and mounted vertically above the first set and offset with respect to the first set so as to enhance smooth rotation of the shaft construction and vanes about a substantially vertical axis. Third (or more) such sets may also be provided.
According to another embodiment of the invention, a Savonius vertical axis wind rotor is provided (that is preferably, although not necessarily, omni-directional) comprising: First and second curved vanes having remote substantially vertical edges widely spaced from each other, and proximate substantially vertical edges more closely horizontally spaced from each other and horizontally overlapping. And, a single substantially vertical central perforated shaft operatively connected to the vanes and adjacent the proximate edges thereof, and mounting the vanes so that, during use, there is spillover of wind from one vane proximate edge to another vane during powered rotation of the vanes in response to wind.
The rotor may be in combination with a mount which mounts the shaft construction and vanes for rotation about a substantially vertical axis, and for operative connection of the shaft construction to a powered element, to provide a wind turbine; and the mount may be adjacent a bottom portion of the shaft construction so that the wind turbine is substantially devoid of a top mount for the rotor. In one embodiment the mount comprises a solid wall continuation of the perforated shaft.
According to yet another embodiment of the invention there is provided a Savonius vertical axis wind turbine rotor comprising: First and second at least partially curved vanes having remote edges widely spaced from each other, and proximate edges closely spaced from each other, the vanes of flexible, collapsible, material. First and second sets of a plurality of substantially rigid substantially radially extending at least partially curved spokes operatively connected to the first and second vanes, respectively, at least one spoke of each set having a collar adjacent the proximate edge of the vane with which it is associated. First and second horizontally spaced substantially vertical rotatable central shafts operatively connected to the first and second sets of spokes, respectively, the collars substantially surrounding the shafts so that the spokes are movable along the shafts from a position in which the vanes are operative to a position in which the vanes are collapsed. And, the shafts mounting the vane proximate edges so that they are overlapped and so that there is spillover from one vane proximate edge to another vane during rotation of the vanes.
According to yet another embodiment there is provided an omni-directional Savonius vertical axis wind turbine rotor comprising: First, second, and third curved vanes each having remote substantially vertical edges widely spaced from each other, and proximate substantially vertical edges more closely horizontally spaced from each other and horizontally overlapping. And a substantially vertical central shaft construction operatively connected to the vanes and mounting the vanes adjacent the proximate edges so that, during use, there is spillover of wind from the proximate edge of each vane to another vane during powered rotation of the vanes in response to wind.
Details of this embodiment, or combinations with this embodiment, may be as described above with respect to the first mentioned embodiment, such as the provision of three substantially vertical shafts.
It is the primary object of the present invention to provide a highly efficient Savonius vertical axis rotor, and wind turbine constructed using the rotor, that has enhanced features while retaining all, or substantially all, of the advantages of a conventional Savonius. This and other objects of the invention will become clear from a detailed inspection of the application and the appended claims.